The present invention relates to a paste for formation of a ceramic capacitor electrode.
Capacitors are an electronic part in which a dielectric layer placed between two electrode layers is allowed to have an electrostatic capacity. As shown in FIG. 1, a capacitor 1 has a structure in which two electrode layers 3 are placed on the upper and lower surfaces of a dielectric layer 2. In recent years, ceramic capacitors using a ceramic dielectric made of barium titanate (BaTiO3) or the like have been used in order to impart heat resistance, corrosion resistance, etc. to a capacitor.
To meet a demand for smaller electric appliances, capacitors have become smaller as well. Nowadays, it is a general trend that such small ceramic capacitors use, as the electrode layer, a film formed with a paste and moreover, in order to achieve a small size and yet a large capacity, employ a laminated structure such as shown in FIG. 2.
Conventional ceramic capacitors, however, have been insufficient in adhesivity of electrode layer film to dielectric layer; therefore, they have had a problem of gradual peeling of electrode layer from dielectric layer upon use.
Peeling of electrode layer from dielectric layer results in formation of a gap between electrode layer and dielectric layer, and an air layer low in dielectric constant comes to be present in the gap. As a result, the capacity of the capacitor is deteriorated with time for the above reason, and the capacitor becomes unable to exhibit its intended function.
Also, conventional ceramic capacitors have, in some cases, through holes in the electrode layer. Owing to the difference in sizes of these through holes, the effective electrode area of capacitor (which determines the capacity of capacitor) varies between capacitors. As a result, the capacity of a capacitor differs greatly between capacitors and there has been an inconvenience of low yield of capacitor properties.
When a ceramic capacitor of laminated structure is produced, there are formed, on a dielectric layer (which later becomes one end of the laminated capacitor produced), electrode layers and dielectric layers by turns, followed by one-time firing of the resulting laminate. At this time, when each electrode layer interposed between two dielectric layers has through holes, the air present in the through holes and the gas generated during the firing expand in the holes during the firing and raise the internal pressures of the holes; as a result, interlayer peeling between dielectric layer and electrode layer takes place. Consequently the dielectric layers give rise to blistering and cracking, and also there has been a problem of a reduction in yield of ceramic capacitor produced. This problem can be solved by carrying out firing for a long time; however, such firing incurs increases in running cost and lead time, resulting in a higher production cost.
The present invention has been made in view of such a situation. The object of the present invention is to provide a paste for formation of a ceramic capacitor electrode, capable of forming an electrode layer of the ceramic capacitor which hardly peels from the dielectric layer of the capacitor and giving an increased capacitor yield in production of ceramic capacitor.
According to the present invention, there is provided a paste for formation of a ceramic capacitor electrode, composed of 10 to 14% by weight of an organic vehicle and 86 to 90% by weight of a platinum powder, wherein the platinum powder contains, in 100% by weight of the powder, 54 to 60% by weight of a spherical particle powder, 36 to 40% by weight of a flaky particle powder and 0 to 10% by weight of an indefinite particle powder.